Electrical heating element



Feb. 11, 1969 w, G. MTHESON ETAL l 3,427,547

ELECTRICAL HEATING ELEMENT Filed Dec. 30, 1965 a I I Il 1 THEODORE J.PRICENSKI WILFRID G. MATHESON INVENTORS ATTOR EY United States Patent O3,427,547 ELECTRICAL HEATING ELEMENT Wilfrid G. Matheson, Marblehead,and Theodore J. Pricenski, Ipswich, Mass., assignors to SylvaniaElectric Products Inc., a corporation of Delaware Filed Dec. 30, 1965,Ser. No. 528,324 U.S. Cl. 338-208 9 Claims Int. Cl. H01c 3/00 ABSTRACT FTHE DISCLOSURE Preventing distortion or warping of the edges of aselfsupporting, plexus-type heating element is accomplished by turningan edge of the plexus back upon the plexus to form a less-warpable rib.

The present invention relates to electrical heating elements and inparticular to self-supporting heating elements comprising a plexus ofrefractory metals `such as molybdenum, tantalum, rhenium, columbium andtungsten.

Refractory metal heating elements fabricated from sheet materials ormachined from heavy stock are known to the art. However, the metal in aheating element of this type does not have crystal structures whichresist element breakage or aid in the maintenance of element geometry.

A solution for these problems is described in United States Patent No.3,178,665, issued on Apr. 13, 1965, to Matheson et al. In that patentare disclosed heating elements, having electrical characteristicsidentical to those or prior art heating elements, but whose structuralcharacteristics are far superior to those of sheet material and machinedstock heating elements.

In particular, the heating element disclosed in this patent is aforaminous plexus comprising a series of intertwisted, elongated,helical convolutions of refractory metal wires. To form the plexus, anumber of helically convoluted Wires, each havijng similar electricalcharacteristics, are intertwisted together in such a way that,generally, two convolutions are intertwisted in each other convolutionexcept for the iirst and last. convolutions of the series, Where onlyone convolution is intertwisted.

One or more of such plexuses are assembled to fabricate a completeheating unit which satises the design requirements of a particularelectrical furnace. The heat output of such heating unit is a directfunction of the size of the plexus used.

However, because of the high temperatures prevalent in furnace operationand because of the action of electrically generated mechanical forces onthe plexuses, the edges of the plexuses may be permanently warped ordistorted.

It is, therefore, an object of the present invention to provide aheating element, of the aforesaid type, capable of withstanding fairlylarge thermal shocks and electrically generated mechanical forces,Without exhibiting permanent destructive physical deformation.

In accordance with the present invention, a heating element for use inan electric furnace comprises a foraminous plexus of an intertwistedseries of helical convolutions of refractory metal wires. The turns ofeach of the wires are held by the turns of an adjacent wire and at leastone edge of the plexus is folded and secured to the plexus at pointsintermediate the edges.

Many other objects, features and advantages of this invention becomemanifest to those conversant with the art, upon making reference to thefollowing detailed description of the invention taken with reference tothe drawings, of which:

FIGURE 1 is a perspective view of an electrica] heating unitparticularly designed for use in a three-phase-powered electricalfurnace; and

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FIGURE 2 is a plan section taken through one of the heating elements orforaminous plexuses, at the section line 2-2.

One embodiment of a heating unit constructed in accordance with thepresent invention comprises a plurality of heating elements 10, 11, 12.Each heating element is an elongated forarninous plexus of anintertwisted series of helical convolutions of refractory metal wires,for example helically convoluted wires 13 to 22. The turns of one wire,for example, turns 13a of wire 13, (one such turn being shown in FIGURE2) are held by the turns 14a of an adjacent wire 14.

Moreover at least one of the edges 10a, 11a, 12a, 12b of each plexus 10,11 and 12, respectively, is folded and secured to the body of the plexusat points intermediate the edges of that plexus.

In particular as shown in FIGURE 2, each plexus edge comprises aplurality of wires at the beginning (or end) of the intertwisted series,for example, wires 17 to 22. The edge is folded and secured to the bodyof the plexus at points intermediate the edges and by means of ahelically convoluted refractory metal wire 23 which engages and holdsthe helical convolutions in one of the wires in the aforesaid plurality,for example convolutions 22a of wire 22, and the helical convolutions16a of a wire 16 intermediate the edges.

Use of a wire 23 having helical convolutions 23a makes the fabricationof a heating element 10, 11, 12 very simple, since the Wire 23 may beturned, as a screw, into the convolutions 16a and 22a of wires 16, 22.However, other means for securing the folded edges of the plexus topoints intermediate the edges, such as for example, wires havingnonhelical convolutions or single wire loops used at the top, bottomand/or midpoints of the folded edges, should be readily apparent tothose skilled in the art.

The heating elements 10, 11, 12 may be assembled in a cylindricallyshaped unit by fastening their lower ends to a cylindrical conductingring 24. The other ends of plexuses 10, 11, 12 are fastened andinsulated from each other by means of conducting arms 25, 26, 27 forconnecting each plexus to a power supply, for example, a source of threephase electrical power. In making such electrical connectionscylindrical ring 24 serves as a common node.

In the preferred embodiment of the aforesaid heating unit, therefractory metal used is tungsten. By folding at least one of the edgesof each plexus away from the edges of adjacent plexuses, the interactionof electrically generated mechanical forces on the plexuses is minimizedat those places where such forces in prior art heating units tended todo most damage, that is, the adjacent edges.

Furthermore, this minimization of destructive mechanical forces isaccomplished without decreasing the heating capacity of the plexus.

While there is shown and described herein certain specific structureembodying the invention, it will be manifest to those skilled in the artthat various modifications and rearrangements of parts may be madewithout departing from the spirit and scope of the underlying inventiveconcept and further that this concept is not limited to the particularforms herein shown and described, except insofar as indicated by thescope of the appended claims.

As our invention we claim:

1. A heating element for use in an electric furnace comprising: anelongated foraminous plexus of an intertwisted series of helicalconvolutions of refractory metal Wires, the turns of one of said Wiresbeing held by the turns of an adjacent Wire, at least one of the edgesof said plexus being folded and connected to the body of said 3 plexus,the fold being connected to said plexus at points intermediate theedges.

2. The heating element according to claim 1, in which each of said edgescomprises a plurality of said wires at the beginning and at the end,respectively, of said intertwisted series.

3. The heating element according to claim 2 in whic at least one of saidedges is secured to said plexus by helically convoluted,refractory-metal wire means for holding the helical convolutions of oneof said plurality of wires and the helical convolutions of one of saidWires intermediate said edges.

4. An electrical heating unit comprising: an elongated plexus of anntertwisted series of helical convolutions of refractory metal wires,the turns of one of said wires being held by the turns of an adjacentwire, at least one of the edges of said plexus being folded andconnected to the body of said plexus, the fold being connected at pointsintermediate said edges; and means for connecting said plexus to a powersupply.

5. The electrical heating unit according to claim 4 in which each ofsaid edges of said plexus comprises a plurality of said wires at thebeginning and at the end, respectively, of said ntertwisted series.

6. The electrical heating unit according to claim 5 in which at leastone of said edges is secured to said plexus by helically convoluted,refractory-metal wire means for holding the helical convolutions of oneof said plurality of wires and the helical convolutions of one of saidWires intermediate said edges.

7. An electrical heating unit comprising: a plurality of heatingelements, each of which is an elongated foraminous plexus of anntertwisted series of helical convolutions of refractory metal wires,the turns of one of said wires being held by the turns of an adjacentwire, at least one of the edges of said plexus being folded andconnected to the body of said plexus, the fold being connected to saidplexus at points intermediate said edges; and means for connecting saidheating elements to a power supply.

8. The electrical heating unit according to claim 7 in which each ofsaid edges of said plexus comprises a plurality of said wires at thebeginning and at the end, respectively, of said ntertwisted series.

9, The electrical heating unit according to claim 8 in which at leastone of said edges is secured to said plexus by helically convoluted,refractory-metal wire means for holding the helical convolutions of oneof said plurality of wires and the helical convolutions of one of saidwires intermediate said edges.

References Cited UNITED STATES PATENTS 3,178,665 4/ 1965 Matheson338-208 3,274,374 9/ 1966 Matheson 338-208 FOREIGN PATENTS 599,394 6/1934 Germany.

BERNARD A. GILHEANY, Primary Examiner.

HAROLD BROOME, Assistant Examiner.

